Chapter 24: Studying the Sun

24.3 The Sun

� There are 100 billion stars in the Milky Way

� The Sun is Earth’s primary source of energy

� Compared to other stars, the Sun is an “average” star.

Structure of the Sun

� The sun can be divided up as

follows:

� Interior

�Surface (Photosphere)

�Atmosphere

�Chromosphere

�Corona

The Interior� Deep inside the interior, the sun

produces energy by nuclear fusion

� Four hydrogen nuclei are converted into the nucleus of a helium atom

� Tremendous energy is released

� Some matter is actually converted to energy

The Interior� Know E = mc2

� As hydrogen is consumed, the product of this reaction—helium—forms the solar core, which continually grows in size.

� The sun has enough fuel to last another 100 billion years.

The Surface (Photosphere)

� The photosphere radiates most of the sunlight we see and can be thought of as the visible “surface” of the sun

� Has granules

� 90% of the surface atoms are hydrogen

The Atmosphere—Part 1--Chromosphere

� Appears as a red rim around the sun

� Thin layer

� Observable for a few moments during a solar eclipse

The Atmosphere—Part 2--Corona

� Outermost part of the atmosphere

� Also visible only during an eclipse—produces a glow

� Produces the solar wind

The Active Sun--Sunspots� Dark regions on the surface of the

photosphere are called sunspots

� They appear dark because they are cooler than the surrounding surface

The Active Sun--Prominences

� Prominences are huge cloudlike structures consisting of gasses

� They often appear as great arches that extend well into the corona

� Prominences are ionized gases trapped by magnetic fields that extend from regions of intense solar activity.

The Active Sun—Solar Flares� Solar flares are brief outbursts that

appear above a sunspot cluster

� They release a large amount of energy

� They are relatively rare

� They produce auroras